The invention relates to a control device for the load-dependent connection of a hydraulic stand-by motor to a base-load motor.
In ground-boring machines with a hydraulic rotational drive, e.g. rock drilling and gimlet machines, it is known to drive the drilling shaft with a rotational drive having two hydraulic motors. Normally, only one of the motors, i.e. the one forming the base-load motor, is activated. If the resistance against rotation increases so that the base-load motor is no longer able to provide the necessary torque, a stand-by motor is switched on which supports the base-load motor in such cases. Usually, both motors are of the same construction and have the same capacity. Both motors are permanently engaged with the same gear wheel of the rods to be rotated. The control device for connecting the stand-by motor consists of a manually operable valve arranged near both engines. In order to operate the control device, the operator must walk up to the control device disposed near the motors and switch it over. If the motors are arranged on a carriage that is displaceable along a derrick, an operator will have to climb the derrick in order to operate the control device. This is not only time-consuming and expensive, but also hazardous.